1. Field of the Invention
The present invention relates to a method of removing thiourea, NH.sub.2 CSNH.sub.2, from spent hydrochloric acid cleaning solvents. More specifically, the present invention relates to chemically oxidizing a thiourea containing solution into inert compounds using a two-step process involving an alkaline solution of an oxidant such as hydrogen peroxide, or ozone followed by the addition of sodium hypochlorite.
2. Description of the Prior Art
Thiourea is used as a copper complexing agent with inhibited hydrochloric acid for simultaneous removal of iron oxide and copper oxide scales from the interior surfaces of industrial equipment and the like. Since thiourea is a suspected carcinogen in laboratory rodents, it has been defined by the RCRA (Resource Conservation and Recovery Act) and the EPA (Environmental Protection Agency) Clean Water Act as a "hazardous substance". Therefore the removal of thiourea by chemical oxidation and/or chemical adsorption is essential to the industrial cleaning business.
At present, thiourea containing solutions are treated by either (1) thermal decomposition using sodium hydroxide at high temperature (e.g., 250.degree. F.) over a prolonged period of time (e.g., 4 days) or (2) reacting with sodium hypochlorite. The disadvantages of these prior art methods include the cost and delay associated with the thermal decomposition process and the fact that the thiourea/sodium hypochlorite reaction forms hazardous chlorinated organic compounds.